Method of forming contact bumps in contact pads

Abstract

A process for forming a contact bump in an electrically conductive contact pad having top and bottom surfaces supported on a dielectric substrate that includes the steps of removing a portion of the substrate underlying the contact pad to form an aperture and expose a portion of the bottom surface of the pad; upwardly deforming the pad by applying force to its exposed bottom surface to form the bump; and filling the aperture behind the bump with a supporting substance.

We claim: 
     
       1. A process for forming a contact bump in an electrically conductive contact pad having top and bottom surfaces supported on a dielectric substrate comprising the steps of removing a portion of said substrate underlying said contact pad to form an aperture and thereby expose a portion of the bottom surface of said pad;   upwardly deforming said pad by applying force to its exposed bottom surface to form said bump; and   filling said aperture behind said bump with a supporting substance.   
     
     
       2. The process of claim 1 comprising removing said portion of said substrate by ablating with a laser. 
     
     
       3. The process of claim 1 wherein said deforming step comprises stamping the exposed bottom surface of said pad with a stamping die to form said bump. 
     
     
       4. The process of claim 1 wherein said filling step comprises dropping an adhesive dielectric material in said aperture in a manner to cause said adhesive dielectric material to fill said aperture. 
     
     
       5. The process of claim 1 wherein said filling step comprises dropping a non-adhesive dielectric material in said aperture in a manner to cause said non-adhesive dielectric material to fill said aperture. 
     
     
       6. The process of claim 1 wherein said aperture is large relative to the size of said contact pad, extends through the entire thickness of said substrate on either side of said pad, and is sufficient to accommodate an impact forming tool. 
     
     
       7. The process of claim 1 wherein said filling step comprises laminating an adhesive-coated cover film to said substrate into or over said aperture and causing said adhesive to flow into said aperture. 
     
     
       8. The process of claim 1 further comprising providing a patterned mask layer underneath said substrate for determining the location of said aperture. 
     
     
       9. A contact bump in an electrically conductive contact pad having top and bottom surfaces supported on a dielectric substrate prepared by removing a portion of said substrate underlying said contact pad to form an aperture and thereby expose a portion of the bottom surface of said pad;   upwardly deforming said pad by applying force to its exposed bottom surface to form said bump; and   filling said aperture behind said bump with a supporting substance.   
     
     
       10. A process for forming a contact bump in an electrically conductive contact pad having top and bottom surfaces supported on a dielectric substrate comprising the steps of removing by ablating with a laser a portion of said substrate underlying said contact pad to form an aperture and thereby expose a portion of the bottom surface of said pad, the difference in interaction between said substrate being removed and the substance of said pad enabling said ablation to leave said pad intact despite exposure to said laser;   upwardly deforming said pad by applying force to its exposed bottom surface to form said bump; and   filling said aperture behind said bump with a supporting substance.   
     
     
       11. A printed circuit comprising at least one printed circuit trace terminating in a metal pad supported upon a preformed substrate, in an intermediate portion of the pad said substrate defining an aperture over which said pad bridges, said pad having an outwardly extending bump form, and a supporting substance disposed within said aperture and adhered to the underside of said bump form-pad and the walls of the substrate bounding said aperture. 
     
     
       12. The printed circuit of claim 11 having a plurality of said pads, a single aperture in said substrate extending under said pads, and said supporting substance extending continuously under said pads, in supporting relationship to said plurality of bumps. 
     
     
       13. The printed circuit of claim Il wherein said circuit is a flexible printed circuit. 
     
     
       14. The printed circuit of claim 12 wherein said circuit is a flexible printed circuit.